1. Field of the Invention
This invention relates to vehicle snow chain systems which may be both rapidly deployed and rapidly retracted. More particularly, it relates to chain attachment devices for such systems.
2. Description of Related Art
Rapidly-deployable snow chain systems, which may be characterized generally as systems which fling short chain segments beneath a road tire, have been known for more than 85 years. Such a system is disclosed in U.S. Pat. No. 1,045,609 and in German Pat. No. No. 266,487 to W. H. Putnam for an ANTISKIDDING DEVICE. Throughout the years, various modifications and improvements have been made by numerous inventors. The following list is a representative list of a dozen other U.S. patents issued in this field:
U.S. Pat. No. 1,150,148 for a TRACTION AND ANTISKIDDING DEVICE; PA1 U.S. Pat. No. 1,223,070 for an ANTISKIDDING DEVICE FOR VEHICLES; PA1 U.S. Pat. No. 1,374,252 for an ANTISKID DEVICE FOR AUTOMOBILES; PA1 U.S. Pat. No. 1,381,001 for a NON-SKID DEVICE FOR MOTOR AND OTHER VEHICLES; PA1 U.S. Pat. No. 1,975,325 for an ANTISKID CHAIN AND MEANS FOR APPLYING AND REMOVING SAME; PA1 U.S. Pat. No. 2,241,923 for an AUTOMATIC EMERGENCY TRACTION DEVICE FOR AUTOMOBILES; PA1 U.S. Pat. No. 2,264,466 for an ANTISKID DEVICE FOR VEHICLES; PA1 U.S. Pat. No. 2,277,036 for an ANTISKID DEVICE; PA1 U.S. Pat. No. 2,283,948 for an AUTOMOBILE TRACTION DEVICE; PA1 U.S. Pat. No. 2,442,322 for an ANTISKID DEVICE; PA1 U.S. Pat. No. 4,299,310 for an ANTISKID DEVICE FOR MOTOR VEHICLES; and PA1 U.S. Pat. No. Des. 286,524 for ANTI SKID CHAIN UNIT FOR VEHICLE TIRES.
Referring now to FIG. 1, a modern rapidly-deployable snow chain system 100 is depicted in its deployed configuration in this rear elevational view drawing. The snow chain system 100 is removably affixed to a drive axle 101 which incorporates a differential unit 102. Inner and outer road wheels (103A and 103B, respectively) are mounted on the visible half of the drive axle 101. On each road wheel (103A and 103B) is mounted a rubber tire (104A and 104B, respectively). The chain system 100 includes a friction drive disc 105 to which a plurality of chain segments 106A, 106B and 106C are attached. Chain segment 106A is depicted as being below the road surface 114, which is normally covered with a layer of snow or ice when the chain system 100 is in the deployed configuration. The friction drive disc 105 is rotatably mounted on a spindle 107 which is affixed to a support member 108 which is pivotally mounted to a mounting bracket 109. The mounting bracket is, in turn, bolted to the suspension spring shackle 113 which secures the suspension leaf springs 112 to the drive axle 101. The chain system 100 also includes a pneumatic cylinder 110 that is bolted to the mounting bracket 109. The pneumatic cylinder 110 has a slidable piston 111 that is held in a normally retracted position within cylinder 110 by spring biasing when pressure within cylinder 108 equals ambient pressure. The outer end of piston 111 is connected to support member 108. In the deployed configuration, the outer rim of friction drive disc 105 is pressed against the sidewall of tire 104A by a biasing force applied to support member 108 by piston 111. The biasing force is provided by pneumatic pressure inside pneumatic cylinder 110 which overcomes the spring biasing and causes piston 111 to extend. As the tire 104A rotates, the friction drive disc 105 also rotates with the chain segments 106 extended more or less radially therefrom. Thus each chain segment 106 is flung, sequentially, beneath the tread portion of tire 104A. In order to retract the system and disengage the friction drive disc 105 from contact with the sidewall of tire 104A, pneumatic pressure to pneumatic cylinder 110 is cut off, causing piston 111 to retract within cylinder 110 and raising the support member 108, the rotatably attached friction drive disc 105 and the attached chain segments 106. In the retracted configuration, the chain segments 106 do not touch the road surface 114.
Several friction drive disc designs are presently in use. As a particular friction drive disc design places constraints on the design of chain segment attachment devices, it is not surprising that there are several types of chain segment attachment devices. FIGS. 2, 3 and 4 depict various views of one type of friction drive disc 200. This type of friction drive disc 200 has a planar upper surface 201 and a pattern of bolt holes 202 which penetrate and are perpendicular to the planar surface 201. The friction drive disc 200 has a molded-on plastic or rubber rim 203 that rides on the sidewall of a tire 104A during deployment (see FIG. 1), causing the friction drive disc 200 to spin and sequentially throw chain segments beneath the tire. The rim 203 has a tread pattern which facilitates the transfer of rotational energy from the tire 104A to the friction drive disc 200 through frictional contact. The friction drive disc assembly 200 also has a cylindrical bearing cavity 204 in which one or more roller bearing assemblies (not shown) are secured with a snap ring (not shown) that fits within snap-ring groove 205. A hole 206 is sized and threaded to accept a Zerk fitting, through with grease may be injected into the roller bearing assemblies. A ring-shaped chain segment retaining plate assembly 500 is bolted to the planar surface 201 with bolts 501. Each chain segment (not shown, but identical to 106A, 106B and 106C of FIG. 1) has a final U-shaped link 502 that is welded to a ring-shaped laminar plate 503. Although the assembled friction drive disc 200 and chain retaining plate assembly 500 is strong and durable, it suffers from the drawback that individual chain segments (not shown) cannot be replaced without removing all of the bolts 501, the entire chain retaining plate assembly 500, cutting or grinding off the U-shaped link 502 that secures the defective chain segment to the plate assembly 500, and rewelding a new U-shaped link 502 with a new attached chain segment in the proper location on the chain retaining plate assembly 500. Without access to a grinder and welding equipment, replacement of a single chain segment is impossible.
Though not shown in this disclosure, another type of friction drive disc has been used in the industry. Each chain segment has a final U-shaped link that is welded to a more-or-less rectangular laminar metal plate which fits snugly within a recess that has been either cast or machined on the lower surface of the friction drive disc. Each rectangular laminar plate is bolted to the friction drive disc with a single bolt. Although each of the mounted chain segments can be individually replaced by removing a single bolt, the drawbacks to this design are greater complexity (the friction drive disc must receive additional machining in order to create the recesses) and wear of the recesses caused by pivoting of the rectangular plates about their respective retaining bolts. As the recesses wear, the magnitude of plate pivot increases, as does the rate of wear. Eventually, the friction drive disc will have to be replaced.
What is needed is a new type of chain segment retaining plate assembly which will fit the type of friction drive disc depicted in FIGS. 2, 3 and 4, and which combines the advantages of both types of assemblies, but none of the drawbacks of either.